Even as the nation's network carriers began reporting billions in second-quarter losses last week, a furious rally drove share prices up by 45 to 60 percent. The market shrugged off the $1.4 billion loss reported by the parent of American Airlines, the nation's largest carrier, and ran its stock up 59 percent. The nation's second-largest airline, United, will report losses in the $3 billion range this week, yet its shares climbed 58 percent.

Why the irrational aeronautic exuberance? Last week's unprecedented decline in the price of oil, which plummeted more than $16 and closed around $130 a barrel. With fuel now accounting for about 40 percent of the airlines' costs, sharply lower oil prices surely looked like good news to the markets.

But irrational exuberance is nothing if not irrational. The biggest airlines-American, United, Delta, Northwest, Continental and US Airways-can't make money at $130 a barrel. They can't make money at $100 a barrel, either. Nor can their smaller competitors. Even the double-digit cuts in passenger capacity and triple-digit aircraft retirements planned for the fall probably won't restore profitability unless oil drops to about $80. (That's what oil sold for late last summer, the last time the big carriers were consistently profitable.) And since both business- and leisure-travel demand is falling, the price hikes and fee increases announced with metronomic regularity this spring and summer are likely to be offset by fall and winter fare sales.

"Don't you dare rain on my parade," an airline executive snapped at me Friday evening. "I want one weekend this summer when I can fantasize about not being in bankruptcy next year."

I hope he enjoyed his weekend, because that brutal reality-every U.S. carrier except Southwest Airlines faces bankruptcy and possibly even liquidation-cannot be ignored. None are sufficiently hedged against triple-digit oil prices. None can ground planes or lay off staff fast enough to keep their corporate heads above the rising tide of red ink. And there's no playbook to consult.

Think I'm being irrationally pessimistic? Tell it to Fitch Ratings, which says there could be "multiple bankruptcies and liquidation" among the major airlines next year. "The industry's current structure is unsustainable in the current fuel environment," Fitch said last week. And if you don't like analysts analyzing, listen to Virgin Group's Richard Branson, whose own worldwide airline empire is shaky. He predicts "spectacular casualties" among the big carriers in the next 12 months.

Perhaps most frightening is that no one can agree on which of the carriers are most at risk. Last Friday, for example, J.P. Morgan Chase double-jumped United shares to "overweight" from "underweight," primarily because the lead analyst thought the airline would announce a big new borrowing scheme this week along with its second-quarter loss. But just hours later, Moody's cut United's debt rating two steps to "Caa1," seven notches below investment grade.

What's the chaos mean in the long term for business travelers? To be honest, I don't know. Even 30 years of plopping myself down in seat 2B isn't particularly preparatory or enlightening. And the longer oil prices remain in triple digits, the less the lessons of the 1990 to 1995 period seem revelatory.

But I can offer several watch-your-back tips for the next several months on the road.

Confirm Your Flights
If you've booked travel for any time after Labor Day, make sure your flights are still on the schedule. Airlines have dropped routes without notice all summer, but the big tranche of cancellations begins on September 2. Overnight, most carriers will shrink their schedules 5 to 15 percent . Even if your airline will still fly on your route, it may have cut frequencies, so check that it has "protected" you on another flight and remembered to match up your onward connections.

Avoid Smaller Airports
The airlines are weeding out service to smaller airports, partially because they bring the least traffic into their hubs and also because the routes are flown with inefficient regional jets. If possible, book flights from the closest hub instead.

Expect Less Help
As they scramble to cut costs, airlines are thinning their already depleted ranks of front-line airport employees. That'll mean longer waits to check in, check bags, and load passengers and luggage onto planes. Carriers are also chopping mechanic jobs, so there will be more delays and cancellations for mechanical reasons. And wherever they had staffed flights above the federally mandated minimums, they are reducing the number of flight attendants. That means even less in-flight service.

Have a Plan B-and a Plan C
Although wags now openly speculate on the survival odds of one carrier or another-Midwest, Frontier (already operating in Chapter 11), US Airways, Sun Country and Spirit seem to be popular picks in death pools-I wouldn't assume any carrier will fold. Or survive. Know your options for every flight you book. And carry your Plan B and Plan C with you in case your carrier folds while you're on the way to the airport. Seriously.

Drain Your Mileage Programs
Finally, stop "banking" frequent-flier miles. If you've got enough miles to claim an award, use them now. The value of miles is depreciating even faster thanks to the route cutbacks and new fees imposed when you redeem an award. Besides, if your airline collapses, there's no guarantee that another carrier will step in and honor unused miles.

The Fine Print.
Midwest Airlines, the Milwaukee-based boutique carrier, is the latest to slash its operations. It announced on Sunday that it would contract its overall capacity by upward of 40 percent. By September, it will have grounded about a third of its aircraft and cut a dozen cities off its route map.